According to Louis L'Amour there probably never was a case where a small band of outlaws treed a town. Consider that there was probably a gun within arm's reach of every able bodied man in town and they were pretty much all civil war veterans.

Also the Code of the West pretty much only said you didn't kill a man who was unarmed or who didn't know you were after him. If a man had a fighting beef with someone he would tell him to "go heel yourself". After that the folks pretty much considered you were warned. If you were told that, you could arm yourself with a 12 gauge and if you were lucky enough to get a shot at the fellow's back that was "fair game".

Stand up gunfights in the street were rare. Sometimes they were employed by professionals to "prove" it was a fair fight.

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Luke 22:36